Magnetic disc having a magnetic layer with a glass transition temperature of at least 75° C. which contains magnetic metal powder of specified pH and surface area

Abstract

A magnetic disc having excellent running durability is disclosed, which comprises a non-magnetic support and a magnetic layer on the non-magnetic support, the layer being composed mainly of a ferromagnetic metal powder and a binder resin, wherein the ferromagnetic metal powder has a pH value of less than 7.0 and a specific surface area as determined by the BET method of at least 40 m 2 /g, and the glass transition temperature of the magnetic layer is at least 75° C.

What is claimed is: 
     
       1. A magnetic disc comprising a non-magnetic support and a magnetic layer on the non-magnetic support, wherein said magnetic layer is comprised of a ferromagnetic metal powder and a binder resin, and wherein said ferromagnetic metal powder has a pH value of less than 7.0 and a specific surface area as determined by the BET method of at least 40 m 2  /g, and said magnetic layer has a glass transition temperature of at least 75° C. 
     
     
       2. A magnetic disc as in claim 1, wherein the specific surface area is 40 to 60 m 2  /g. 
     
     
       3. A magnetic disc as in claim 1, wherein said ferromagnetic metal powder has a crystal size of no more than 400 Å. 
     
     
       4. A magnetic disc as in claim 1, wherein said ferromagnetic metal powder is selected from the group consisting of Fe, Fe-Co, Fe-Ni and Fe-Ni-Co. 
     
     
       5. A magnetic disc as in claim 1, wherein said ferromagnetic metal powder has a saturation magnetization of at least 110 emu/g and a coercive force of at least 800 Oe. 
     
     
       6. A magnetic disc as in claim 1, wherein said ferromagnetic metal powder has a pH value of less than 6.8. 
     
     
       7. A magnetic disc as in claim 1, wherein said ferromagnetic metal powder has a pH value of at least 5 or more. 
     
     
       8. A magnetic disc as in claim 1, wherein said ferromagnetic metal powder has a pH value of from 5 to 6.8. 
     
     
       9. A magnetic disc as in claim 1, wherein said magnetic layer has a glass transition temperature of from 80° to 160° C. 
     
     
       10. A magnetic disc as in claim 1, wherein said magnetic layer has a glass transition temperature of from 120° to 150° C. 
     
     
       11. A magnetic disc as in claim 1, wherein said magnetic layer has a dried thickness of from about 0.5 to 12 μm. 
     
     
       12. A magnetic disc as in claim 1, wherein said magnetic layer comprises multiple layers. 
     
     
       13. A magnetic disc as in claim 1, wherein said binder resin is a mixture of 30 to 60 wt% of a vinyl chloride copolymer, 10 to 40 wt% of a polyurethane resin, and 20 to 50 wt% of a polyisocyanate. 
     
     
       14. A magnetic disc as in claim 1, wherein said binder resin is a mixture of 30 to 60 wt% of a cellulose derivative, 10 to 40 wt% of a polyurethane resin and 10 to 40 wt% of a polyisocyanate.